CLOSED AIR CIRCULATION SYSTEM

SYSTEME FERME DE CIRCULATION D'AIR

English Abstract

The invention relates to a closed air circulation system for an apparatus used
for sorting wood chips (1), containing chips (11, 12) in a variety of sizes
and/or fines particles (13), in a wood chips processing chamber (17), in
separate fractions by means of a gas flow (4), which is delivered from one or
more nozzle chambers (8, 8') by way of a nozzle slit (3) into the wood chips
processing chamber (17) and which applies an impulse action to the processing-
bound wood chips (1) sliding along an inclined support surface (2). Air is
circulated from the wood chips processing chamber (17) by way of a dedusting
cyclone (18) into said one or more nozzle chambers (8, 8').

French Abstract

L'invention concerne un système fermé de circulation, destiné à un appareil de tri de copeaux de bois (1) contenant des copeaux (11, 12) de diverses dimensions et/ou de fines particules de bois (13), dans une chambre de traitement de copeaux de bois (17), ce tri consistant à séparer des fractions au moyen d'un écoulement de gaz (4), lequel est fourni dans la chambre de traitement (17) des copeaux de bois, à partir de d'au moins une chambre (8, 8') comprenant un ajutage, par la fente de l'ajutage (3), et lequel applique une action d'impulsion sur les copeaux de bois (1) liés par le traitement et coulissant le long d'une surface de support inclinée (2). L'air circule à partir de la chambre de traitement (17) des copeaux de bois, au moyen d'un cyclone de dépoussiérage (18) et pénètre dans au moins une chambre (8, 8') comprenant un ajutage.

Claims

6
Claims
1. An apparatus for sorting wood chips, containing chips in a variety of sizes
and/or fines particles, in a wood chips processing chamber, in separate
fractions by
means of an air flow, which is delivered from one or more nozzle chambers by
way
of a nozzle slit into the wood chips processing chamber and which applies an
impulse action to the wood chips as the wood chips slide along an inclined
support
surface to sort the chips into said separate fractions within the processing
chamber,
said air being circulated from the wood chips processing chamber by way of a
dedusting cyclone into said one or more nozzle chambers, the improvement
comprising:
a closed air circulation system in which air flow from the wood chips
processing chamber to the dedusting cyclone is controlled by an exhaust fan
and air
flow from the nozzle chamber into the processing chamber is controlled by a
nozzle
fan downstream of the exhaust fan;
a pipe arranged between the exhaust fan and the nozzle fan extending from
the dedusting cyclone to the nozzle chamber, wherein said pipe is in direct
communication with an ambient atmosphere; and
a negative pressure in the wood chips processing chamber is maintained at a
predetermined level in dependency on said exhaust fan to regulate the amount
of air
removed from the wood chips processing chamber into the dedusting cyclone.
2. A system as set forth in claim 1, wherein the exhaust fan is positioned in
the
pipe extending from the dedusting cyclone to a chamber in said pipe that is
open to
the ambient atmosphere.
3. A system as set forth in claim 1, wherein the nozzle fan is positioned in
the
pipe extending from the nozzle chamber to a chamber in said pipe that is open
to
the ambient atmosphere.

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4. A system as set forth in any one of claims 1 to 3, wherein said pipe
extending
from the dedusting cyclone to the nozzle chamber in communication with the
ambient atmosphere equalizes transient pressure fluctuations and maintains the
pressure ratio within said system.
5. A system as set forth in any one of claims 1 to 4, wherein said nozzle fan
regulates the pressure in said nozzle chamber.
6. A closed air circulation system for an apparatus that sorts wood chips into
separate fractions by exposing wood chips sliding on an inclined support
surface to
a flow of air from a nozzle slit extending laterally across the support
surface, said
closed air circulation system comprising:
the inclined surface and the nozzle slit;
a wood chips processing chamber substantially enclosing the inclined surface
and nozzle slit;
an exhaust fan arranged to exhaust air from said chamber and maintain said
chamber at a negative pressure with respect to atmospheric pressure;
a dedusting cyclone arranged to receive air exhausted from said chamber;
a nozzle fan generating air flow into a pressurized nozzle chamber in
communication with said nozzle slit to sort the chips into said separate
fractions
within the processing chamber; and
a conduit in communication with said nozzle chamber and said dedusting
cyclone in which exhaust air flows from the cyclone to the nozzle chamber;
wherein said conduit also communicates directly with the ambient
atmosphere, said negative pressure is maintained at a predetermined value by
regulating the amount of air exhausted from said chamber, and said nozzle fan
is
arranged in said conduit between said nozzle chamber and a location where said
conduit communicates with said ambient atmosphere..

8
7. The closed air circulation system of claim 6, wherein said exhaust fan is
arranged in said conduit between said dedusting cyclone and said location
where
said conduit communicates with said ambient atmosphere.

Description

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1
Closed air circulation system
The Invention relates to a closed air circulation system for an apparatus used
for
sorting wood chips, containing chips in a variety of sizes and/or fines
particles, in a
wood chips processing chamber, in separate fractions by means of a gas flow,
which is delivered from one or more nozzle chambers by way of a nozzle slit
into the
wood chips processing chamber and which applies an impulse action to the
processing-bound wood chips sliding along an inclined support surface.
The above type of apparatus is necessarily provided with circulation of air,
on the
one hand because of aspects relating to energy economy, and on the other hand
because of a dust problem. However, operation of the apparatus itself sets
strict
limits to facilities of implementing circulation in order not to cause trouble
for the
apparatus in terms of its operation.
It is desirable to provide a closed air circulation system for the above type
of
apparatus, said air circulation system securing faultless operation of the
apparatus
for its part.
According to the invention, this object is accomplished in such a way that,
and an air
circulation system of the invention is characterized in that air is circulated
from the
wood chips processing chamber by way of a dedusting cyclone into said one or
more nozzle chambers.
According to one aspect of the invention there is provided an apparatus for
sorting
wood chips, containing chips in a variety of sizes and/or fines particles, in
a wood
chips processing chamber, in separate fractions by means of an air flow, which
is
delivered from one or more nozzle chambers by way of a nozzle slit into the
wood
chips processing chamber and which applies an impulse action to the wood chips
as
the wood chips slide along an inclined support surface to sort the chips into
said
separate fractions within the processing chamber, said air being circulated
from the

CA 02420301 2009-02-19
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wood chips processing chamber by way of a dedusting cyclone into said one or
more nozzle chambers, the improvement comprising:
a closed air circulation system in which air flow from the wood chips
processing chamber to the dedusting cyclone is controlled by an exhaust fan
and air
flow from the nozzle chamber into the processing chamber is controlled by a
nozzle
fan downstream of the exhaust fan;
a pipe arranged between the exhaust fan and the nozzle fan extending from
the dedusting cyclone to the nozzle chamber, wherein said pipe is in direct
communication with an ambient atmosphere; and
a negative pressure in the wood chips processing chamber is maintained at a
predetermined level in dependency on said exhaust fan to regulate the amount
of air
removed from the wood chips processing chamber into the dedusting cyclone.
According to another aspect of the invention there is provided a closed air
circulation
system for an apparatus that sorts wood chips into separate fractions by
exposing
wood chips sliding on an inclined support surface to a flow of air from a
nozzle slit
extending laterally across the support surface, said closed air circulation
system
comprising:
the inclined surface and the nozzle slit;
a wood chips processing chamber substantially enclosing the inclined surface
and nozzle slit;
an exhaust fan arranged to exhaust air from said chamber and maintain said
chamber at a negative pressure with respect to atmospheric pressure;
a dedusting cyclone arranged to receive air exhausted from said chamber;
a nozzle fan generating air flow into a pressurized nozzle chamber in
communication with said nozzle slit to sort the chips into said separate
fractions
within the processing chamber; and
a conduit in communication with said nozzle chamber and said dedusting
cyclone in which exhaust air flows from the cyclone to the nozzle chamber;

CA 02420301 2009-02-19
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wherein said conduit also communicates directly with the ambient
atmosphere, said negative pressure is maintained at a predetermined value by
regulating the amount of air exhausted from said chamber, and said nozzle fan
is
arranged in said conduit between said nozzle chamber and a location where said
conduit communicates with said ambient atmosphere.
The wood chips processing chamber is adapted to be maintained at a negative
pressure with respect to atmospheric pressure, such that the inevitable
bleeding
points present in the processing chamber - e.g. outlet ports for conveyors -
do not
release dust to environment. Thus, the arrangement is preferably such that the
wood chips processing chamber has its negative pressure adapted to be
maintained
at a predetermined level by regulating the amount of air to be absorbed from
the
processing chamber into the dedusting cyclone.

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2
In order to maintain pressure ratios in balance, the air to be circulated is
adapted to be circulated through a duct or a chamber open to atmosphere. The
duct or chamber open to atmosphere is preferably included in a pipe extending
from the dedusting cyclone to the nozzle chamber. The pipe extending from
the dedusting cyclone to the duct or chamber open to atmosphere is provided
with a fan for regulating pressure in the processing chamber.
The pipe extending from the duct or chamber open to atmosphere is also pro-
vided with a fan. Thus, pressure in the nozzle chamber is preferably adapted
to
be regulated by means of said fan.
By virtue of said duct or chamber open to atmosphere, transient pressure
fluctuations are equalized with the result that, on the one hand, there will
be no
significant discharges to atmosphere and, on the other hand, the apparatus
performs its operation within set limits.
The invention will now be described in more detail with reference to the accom-
panying drawings, in which:
Fig. I shows in a diagrammatic vertical section an apparatus for sorting
wood chips in a closed processing chamber by the application of
an impulse action.
Fig. 2 shows in a diagrammatic section a closed air circulation system
applied to the apparatus of fig. 1.
Fig. 1 shows schematically an apparatus for sorting wood chips 1 in separate
fractions. Fines particles 13, possibly contained in the wood chips 1, are
sorted
out to form a separate fraction and individual chips 11, 12 are determined by
the thickness thereof as excess thickness chips 11 (reject) and accepted chips
12 (accept).
The apparatus comprises a feeder 6 for supplying the wood chips I onto a
sloping support surface 2 for a substantially single layer. The individual
chips

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11, 12 settle in a natural way on the support surface 2 to rest upon the
largest
surface thereof, i.e. in the case of wood chips, upon the longitudinal/lateral
surface thereof.
The support surface 2 is a solid, plain, and durable flat surface, which forms
a
steeply sloping slide surface for the wood chips 1 to be sorted.
The wood chips 1 emerging from the feeder 6 are first adapted to slide down
the sloping support surface 2 and then over a slit 3 arranged across the sup-
port surface, said slit being adapted to deliver an impulse action 4 directed
away from said support surface 2 and applied to one or more chips 11, 12 or
fines particles 13 presently in line with the slit. The impulse action is
adapted to
be produced by means of a gas flow 4, preferably an air flow. The impulse
action 4 may have a direction which is perpendicular to the support surface 2,
or also at an oblique angle relative to the support surface 2.
The air flow is generated by a fan 7. In order to secure uniformity of the im-
pulse action 4, a nozzle chamber 8 is arranged between the fan 7 and the slit
3.
The varying thickness chips 11, 12 and the eventual fines particles 13 are
adapted to be separated from each other along various trajectories defined by
the impulse action 4 for the particles to be sorted.
The fines particles 13, which are smaller in size than the width of the slit
3,
adopt a maximum deviation of velocity and, thus, are adapted to be diverted by
the action of a baffle/guide plate 14 in a separate fraction into a chute 15.
The individual chips 11, 12, which are substantially larger in size than the
width
of the slit 3 and, thus, heavier than said fines particles 13, adopt a
deviation of
velocity substantially less than that adopted by the fines particles 13 when
present in line with the slit 3. A pressure-generated impulse sends the
individ-
ual chips 11, 12 flying in different trajectories defined by a chip thickness,
and
the flow of chips is divided in separate fractions by means of a separating
wall

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4
5. The averagely minimum thickness chips 12 fly over the separating wall 5
and are further guided to a discharge screw 10. Respectively, the averagely
maximum thickness chips fly a shorter distance and fall into a feeder 6'
present
between the separating wall 5 and the slit 3.
In the illustrated example, the averagely maximum thickness chips 11 received
in the feeder 6' are reprocessed in a lower second apparatus, whereby a frac-
tion thereof (the averagely lightest fraction) is guided over a separating
wall 5'
further onto the discharge screw 10, and another fraction (the averagely heavi-
est fraction) falls into a chute fitted between the separating wall 5' and the
slit 3
and provided with a discharge screw 9.
Processing of the wood chips I is all in all adapted to take place in a
dustproof
processing chamber 17. The discharge of air from the chamber 17 is arranged
through an opening represented by reference numeral 34.
Fig. 2 depicts diagrammatically a closed air circulation system for an
apparatus
as illustrated in fig. 1.
In the solution of fig. 2, air is circulated from the wood chips processing
cham-
ber 17 by way of a dedusting cyclone 18 into nozzle chambers 8, 8'.
The wood chips processing chamber 17 is adapted to be maintained at an
underpressure with respect to ambient air pressure. Thus, eventual bleeding
points present in the processing chamber 17 do not release dust to environ-
ment. The wood chips processing chamber 17 has its underpressure adapted
to be maintained at a predetermined level by regulating the amount of air to
be
absorbed from the processing chamber 17 into the dedusting cyclone 18.
In order to enable the absorption of dust-mixed air uniformly across the
entire
width of the processing chamber 17, the intake opening 34 is adapted to ex-
tend across the entire width of the chamber 17.

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The air to be circulated is adapted to be passed through a duct or chamber 19,
which is in communication with the dedusting cyclone 18 by way of a pipe 20
and with the nozzle chambers 8, 8' by way of pipes 21, 21'.
5 The pipe 20 is provided with a fan 22, whereby pressure in the processing
chamber 17 can be regulated. The fan 22 is used for absorbing dust-bearing
air from the processing chamber 17. The air passes through the deducting
cyclone 18, the dust separating and discharging from the cyclone (an arrow
38).
A fan 7 present in the pipe 21 is used for regulating pressure in the nozzle
chamber 8, and thus the pressure of the gas flow 4 emerging from the slit 3.
Respectively, a fan 7' present in the pipe 21' regulates pressure in the
nozzle
chamber 8'.
By virtue of the duct or chamber 19 open to atmosphere, transient pressure
fluctuations are equalized with the result that there will be no significant
dis-
charges to atmosphere and, on the other hand, the fans 22; 7, 7' do not have
an adverse effect on each other.

Representative Drawing